This application claims the priority of German application 196 48 737.4, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a steering apparatus with a user-operated steering angle input system with corresponding steering shaft and with a hydraulic unit for coupling a steering angle setting system to the steering angle input system. The hydraulic unit comprises a piston-and-cylinder unit which is disposed with a long axis running transversely across the steering shaft and whose axially moving piston is coupled mechanically with the rotatory steering shaft and divides the cylinder into two halves each with a working chamber disposed on the opposite side of the steering shaft. The piston is configured as a dual piston and coupled mechanically with the steering shaft by a coupling section situated between its ends defining the working chambers.
DE No. 195 46 942.9 describes a steering apparatus for motor vehicles with a user-operated steering angle input system with corresponding steering shaft and with a hydraulic unit for coupling a steering angle setting system to the steering angle input system. The hydraulic unit comprises a piston-and-cylinder unit which is disposed with the longitudinal shaft running transversely of the steering shaft. An axially moving piston is coupled mechanically with the rotatory steering shaft and divides the cylinder into two halves each with a working chamber. In normal operation, an electrical coupling is active between the steering angle input system and the steering angle setting system. A motor is coupled to the steering shaft and serves to produce a reverse torque. The steering angle setting system contains a hydraulic unit which is operated by a computer unit detecting the steering shaft position and acting upon the steerable wheels of the vehicle. A hydraulic unit serves as a reserve coupling between the steering angle input system and steering angle setting system to increase safety against failure and is active in the event of failure of the electrical coupling. In this known hydraulic unit, the piston-and-cylinder unit is positioned entirely on one side of the steering shaft, and the cylinder is divided by a narrow piston into the two working chambers. The piston is moved by a piston rod which passes frontally through the cylinder from both ends and is coupled at its extremities to return springs which define an equilibrium center position. In its end portion facing the steering shaft, the piston rod is configured as a rack and coupled mechanically to the steering shaft configured as a pinion in a corresponding area. The hydraulic unit so constructed requires in its lengthwise direction a space of at least six times its stroke.
DE application No. 195 46 733.7 discloses a steering apparatus in which, likewise, in addition to an electrical coupling provided for normal operation, a hydraulic unit is provided as a reserve coupling between the steering angle input system and the steering angle setting system. The hydraulic unit comprises a piston-and-cylinder unit with its long axis running parallel to the steering shaft, through both ends of which the steering shaft passes. In the area within the cylinder, the steering shaft is provided with a screw thread which cooperates with an internal thread of a narrow annular piston surrounding the steering shaft to shift it axially. From the working chambers separated from one another in the cylinder by the piston, a rigid hydraulic line runs transversely of the steering shaft. Thus, it is not easily possible to achieve in this steering system the ability of the steering angle input system to turn together with the steering shaft.
A steering apparatus is disclosed in U.S. Pat. No. 1,615,075. The hydraulic unit contains a connecting line for each working chamber running out from the end part of the particular working chamber which is remote from the steering shaft, away from the steering shaft and then with a bend substantially at right angles to the longitudinal axis of the piston-and-cylinder unit it runs to the steering angle setting system configured as an additional piston-and-cylinder unit.
JP 62-15167 (A) discloses, in a steering apparatus for a motor vehicle, the provision of a hydraulic coupling between the steering angle input system and steering angle setting system as a reserve coupling which is active in the event of failure of an additional, electrical coupling between the steering angle input system and the steering angle setting system.
DE 39 18 987 A1 describes a power assisted steering for motor vehicles in which a steering spindle is connected by a rotary sliding valve to an input member of a steering gear, and a working piston of a hydraulic power boosting device can be fed hydraulic fluid by a servo pump through the control valve in the case of a relative rotation of the steering spindle with respect to the input member. The drive shaft of an electric motor is connected with the rotary valve, and the electric motor can be controlled by a signal from a first sensor responding to a relative rotation of the steering spindle with respect to the input member. Thereby, it produces a counter-force on the rotary valve to counter the rotary movement of the steering spindle. The electric motor thus serves for the production of a reverse torque in the case of active hydraulic coupling of the steering. In addition, the electric motor can be made to boost the steering force in case of failure of the hydraulic power boosting system, i.e., to act as a servo motor.
An object of the present invention is to provide a steering apparatus in which the hydraulic unit requires relatively little space and also is secured against failure and/or is constructed such that, if necessary, it easily permits the steering wheel input system to turn with the corresponding steering shaft.
The foregoing object has been achieved in accordance with the present invention by providing a steering apparatus in which each of the two connecting lines runs from an opening thereof out of the corresponding end of the working chamber substantially parallel to the longitudinal axis of the piston-and-cylinder unit into an area proximate the steering shaft or the hydraulic unit serves as a hydraulic reserve coupling between the steering angle input system and the steering angle setting system, which is active in the event of failure of an additional, electrical coupling between the steering angle input system and the steering angle setting system, and an electric motor is coupled with the steering shaft to produce, when the electrical coupling between the steering angle input system and steering angle setting system is active, a reverse torque and, when the hydraulic unit is active, to be operable as a servo motor.
In the steering apparatus of the present invention, the piston-and-cylinder unit is disposed horizontally with its long axis transverse to the steering shaft such that its cylinder extends on both sides of the steering shaft. The piston is mechanically coupled with the steering shaft by a coupling section which lies between the piston ends which define the working chamber. Thereby, there is no end opening in the cylinder for the passage of a piston rod protruding therebeyond, so that the space required transversely of the steering shaft is limited to the cylinder length. This length can be limited to approximately four times the piston stroke required for the maximum steering angle. The position of the piston-and-cylinder unit with its longitudinal axis perpendicular to the steering shaft additionally facilitates the achievement of a desirable ability of the steering wheel input system to pivot as desired together with the corresponding steering shaft.
Furthermore, the compact construction of the hydraulic unit in accordance with the present invention is further facilitated by running the connecting line for each working chamber from the end of the corresponding cylinder half remote from the steering shaft, substantially parallel to the longitudinal axis of the piston-and-cylinder unit, into an area close to the steering shaft, where it compactly continues along the steering shaft and/or can merge with a section of line affixed to the vehicle's body.
In the steering apparatus according to the present invention, the hydraulic unit serves especially as a hydraulic reserve coupling for an electrical coupling active in normal operation between the steering angle input system and the steering angle setting system. An electric motor coupled to the steering shaft is provided which, when the electrical coupling is active, produces a reverse torque on the steering shaft and can function as a servo motor when the hydraulic unit is active. This is important especially when the steering angle setting system comprises a hydraulic unit and the latter fails. In such a case, the wheels can then be acted upon directly by the hydraulic unit coupled to the steering shaft, assisted by the servo motor with hydraulic fluid, in order to set the desired steering angle.
In the improved steering apparatus of the present invention, the steering angle input system is mounted for pivoting together with the steering shaft about an axis perpendicular to the latter. The two connecting lines to the working chambers of the piston-and-cylinder unit are led each to a corresponding rotary connecting element disposed near the steering shaft, which is disposed horizontally in the pivot axis for rotation about the latter. Thus, the hydraulic fluid can be transferred through the rotary connecting elements between, on one hand, the working chambers of the piston-and-cylinder unit and, on the other hand, the steering angle setting system, without the latter being in conflict with the pivoting ability of the steering angle input system.